The present invention relates to a method of producing protective films which are used as protective covers for photomasks, reticles, or the like and a jig for producing the same and, more particularly, to a method of producing films which is used in peeling off a film formed on a substrate in a production process and in adhering the peeled film to one side surface of a frame, and a jig used for peeling off the film formed.
In recent years, protective films typified by pericles have come to be increasingly provided on photomasks and reticles (hereafter simply referred to as masks) for the purposes of protecting mask pattern surfaces and preventing foreign substances such as dust particles from being deposited thereon. To produce a pericle according to a conventional method, a film is first formed on a substrate by spin coating or the like, is then peeled off, and is adhered on one side surface of a pericle frame. Subsequently, a portion of the film projecting from the pericle frame is cut off.
At this juncture, first of all, the peeling the film off the substrate is conventionally carried out as follows: Pieces of a wide adhesive tape which has a small modulus of elasticity are adhered on a periphery of the film in the shape of #, and the film is peeled off carefully from one side by manually holding the adhesive tape. After the film has been released, the pieces of the adhesive tape provided on both sides of the film are manually held, and the film is placed on a pericle frame with an adhesive applied on side end surfaces thereof and is adhered thereto. Since the film is thin, however, when it is peeled off, the film becomes partially elongated and is hence liable to become damaged unless the film is peeled off at a constant speed and uniformly at portions in a direction perpendicular to the peeling direction. Therefore, it has not been easy to peel off the film uniformly at a constant speed without causing breakage.
Secondly, the adhesion of the film onto the pericle frame is conventionally carried out by holding with both hands the pieces of the aforementioned adhesive tape, adhered in the form of # around the periphery of the film to peel the film off the substrate, and by placing the film on the pericle frame with its side coated with the adhesive facing upward. However, if the film is adhered by being simply placed on the pericle frame, slackness is liable of occur on the film surface, and it is impossible to adhere the film uniformly on the entire surface of the side end surface of the frame, so that foams are liable to enter the adhered portion and an uneven surface is likely to occur. For this reason, it is desirable to install the film on the frame with the film set in a tense state by lightly and uniformly applying tension to the film from the four sides. However, it is not easy to apply tension to the film into a planar configuration in such a manner that excessive tension or slackness are not caused n the film surface. In addition, there are cases where the adhesive applied to the frame is extruded to the inner and outer sides of the frame, and the extruded adhesive causes the film to swell at an edge of the film, as shown in FIG. 9. If there is any such swollen portion, there is the possibility of the film becoming broken at the swollen portion when the pericle is held by a device for installing the pericle on the mask. To apply strong tension to eliminate any swelling of the film due to the extruded adhesive is not desirable since the film is liable to become broken.
Thirdly, the protective films are generally cleaned by air blow at the time when they are produced or used (at the time when they are installed on the mask), and, at that time, the film surface vibrates. However, since the thickness of the pericle film is very small, a fracture is likely to occur due to an edge of the pericle frame.
As other methods of producing protective films, the following methods have been proposed: (1) a method in which a releasable film is formed on a substrate by using a material which is capable of undergoing sol-gel conversion, and a thin film is further formed thereon. This laminate is then immersed in warm water, and the releasable film is subjected to sol-gel conversion to cause the thin film to float in the warm water. Subsequently, this thin film is scooped up from the warm water by means of a frame, and is then subjected to heating and drying (Japanese Patent Laid-Open No. 182730/1984), (2) a method in which after a film is formed on a substrate, a pericle frame with an adhesive applied thereto is pressed against the film to allow the film to become adhered thereto, and, after adhesion, the pericle frame is separated from the substrate together with the film, and (3) a method in which, after a film is formed on a substrate, a frame with an adhesive applied thereto is placed on the laminate so as to be adhered. This structure is immersed in water to separate the film from the substrate, and the frame with the frame secured thereto is lifted up from the water and is then allowed to dry (Japanese Patent Laid-Open No. 237450/1985). However, in cases (1) and (3), it is necessary to dry the film after it is recovered from the water, and these methods cannot be applied to an insoluble film and a film whose surface has been provided with surface treatment with an insoluble substance. Moreover, particularly in the case of the former method in which the thin film floating in the water is scooped up by the frame, creases or slackening are liable to occur in the film surface. In addition, in case (2) above, when the frame is pressed against the substrate, there is the risk of causing damage to the substrate, and the film is liable to become broken during cleaning by the air blow, as described above. Furthermore, the film must be peeled off in such a manner as to be lifted up from the portion where the inner side of the frame is adhered to the end surface of the substrate. However, since the space between the film and the substrate assumes the state of a vacuum, a strong force is required in peeling off the film. Hence, there are cases where the film becomes broken, and the frame is subjected to deformation due to a strong force applied locally.